The mention of diarrhea is likely to elicit a vague squeamishness in the First World, where indoor toilets and clean water for washing are commonplace, but for thousands of children living in drought-plagued sub-Saharan Africa, the subject is one of life and death.
Although the illness is both easily preventable and treatable, World Health Organization data show that close to 920,000 people in the U.N. agency's Africa region died of diarrheal diseases in 2008. Nearly three-quarters of these deaths were children younger than 4, and this region accounts for 40 percent of global deaths from diarrhea in young children.
Climate change could make this problem even worse. A study published last week in the International Journal of Environmental Research and Public Health reveals a direct link between the hotter, drier conditions associated with climate change and an increased incidence of diarrheal diseases in Botswana.
Botswana, a landlocked country north of South Africa, experiences a wet season between November and April and a dry season between May and October. By comparing 30 years of government health facility records with precipitation and temperature data, scientists found that 20 percent more people became sick with diarrhea during the dry season.
Climate change is likely to intensify the dry season conditions linked with diarrhea. Southern Africa could experience temperature rise of up to 4 degrees Celsius by 2080, according to the U.N. Intergovernmental Panel on Climate Change's most recent report, and most models also predict a decrease in rainfall.
"If climate change proceeds as projected ... that will increase the degree to which diarrhea is experienced by communities -- particularly very vulnerable communities," said Kathleen Alexander, lead author of the report and an associate professor of wildlife at Virginia Polytechnic Institute and State University in Blacksburg, Va.
Although the study was restricted to Botswana, Alexander says the outcome would likely be the same in other arid regions, as in the neighboring countries of Namibia and Zimbabwe.
'There's so many flies'
The reason warmer, drier conditions cause a high incidence of diarrhea is not entirely clear. In fact, Alexander was surprised at this result, as many other studies have linked diarrheal diseases with the rainy season. While the researchers did see a peak of diarrhea cases in the rainy season as well, they were puzzled to find that far more cases were reported in October.
But while Alexander was visiting a hospital in Botswana, a local nurse suggested a plausible link:
"She said: 'Well, it's flies, it's flies, that's the problem -- there's so many flies,'" Alexander recalled. "And I got to thinking about that. So I went back and started looking at the literature, and the literature's pretty clear that dry, hot conditions, which characterize October, are very supportive and conducive towards increased fly breeding and activity."
Flies, which often breed in fecal material, are carriers of several diarrheal diseases, like salmonella and cryptosporidiosis. And climate change will not have the same effect on flies as it will on polar bears.
"A recent study identifies that increases in temperatures associated with forecasted climate change will dramatically increase fly population density with M. domestica, for example, increasing 244 percent by 2080 under the worst case climatic scenario, and by 156 percent under the moderately optimistic medium-low emissions scenario," the report states.
Such a link has not yet been proved through research, but Alexander suspects that simple steps to improve hygiene, like placing screens over openings in pit toilets and installing toilet lids, could go a long way to preventing fly-borne diarrheal diseases.
How an inconvenient disease can become devastating
A 2005 report prepared by the U.N. Development Programme showed that although the majority of Botswanans can get safe water, very few of the country's poor have access to adequate sanitation. Alexander, who has lived in Botswana since the late 1980s, said many of the people she works with can't afford the connection fee to access public sewage systems. Many others don't even have access to a pit latrine, she said, and there is often a fee for using a public bathroom facility.
Creating better access to sanitation is generally thought to be the best way to decrease the number of diarrhea cases. "To improve conditions, the emphasis is on encouraging hand washing practice, boiling and/or sieving their drinking water, food warming and prosper disposal of refuse," Charles Berko, general secretary of the African Public Health Network at the Johns Hopkins Bloomberg School of Public Health, explained in an email.
These steps are far simpler than reversing global warming. But if sanitation is not improved in vulnerable communities before the temperature rises, diarrheal disease could become even more devastating, the study said.
"If you look at two things, the climate change effect and the effects of [improved] sanitation and hygiene, sanitation and hygiene will have a larger effect than climate change ever will -- if we can get it on board," Alexander said.
"When you go to these homes and you see people have a reed hut with a dirt floor, they don't have a toilet, their kids are sitting in the soil, and they don't have very much -- there's no resiliency there," she added. "There's an urgent need to address present-day health challenges so we're prepared for these other changes, because the impacts of climate change arise from these existing vulnerabilities."